Hurricane HUMBERTO

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HURRICANE HUMBERTO DISCUSSION NUMBER 18
NWS NATIONAL HURRICANE CENTER MIAMI FL AL092013
1100 PM AST THU SEP 12 2013
MICROWAVE IMAGERY...FROM METOP AND SSMIS...INDICATE THAT THE DEEP
CONVECTION IS BECOMING DISLOCATED FROM THE LOW-LEVEL CENTER OF
HUMBERTO. SO WHILE THE HURRICANE IS STILL PRODUCTING QUITE COLD
CLOUD TOPS...WEAKENING OF THE SYSTEM HAS APPARENTLY BEGUN. THE
INTENSITY OF 70 KT IS A BLEND OF THE HIGHER SUBJECTIVE DVORAK
CURRENT INTENSITY NUMBERS FROM TAFB AND SAB WITH THE LOWER ADT. A
RECENT ASCAT SCATTEROMETER PASS ALSO INDICATED THAT THE CYCLONE
CONTINUES TO GROW LARGER...WITH TROPICAL STORM FORCE WINDS
EXTENDING OUT ALMOST 200 NM FROM THE CENTER IN THE EASTERN
SEMICIRCLE.
THE AFOREMENTIONED DISPLACEMENT OF THE CONVECTION IS BEING CAUSED BY
STRONG SOUTHWESTERLY VERTICAL WIND SHEAR OF OVER 30 KT...PRIMARILY
DUE TO A RATHER ROBUST TROPICAL UPPER TROPOSPHERIC TROUGH TO THE
WEST OF HUMBERTO. THIS STRONG SHEAR SHOULD CONTINUE FOR AT LEAST A
COUPLE OF DAYS...WHICH...IN COMBINATION WITH MARGINAL
THERMODYNAMICS...SHOULD LEAD TO STEADY WEAKENING. AT THE LONGER
TIME RANGE...THE SHEAR IS PREDICTED TO LESSEN DUE TO THE FILLING OF
THE UPPER TROUGH WHILE HUMBERTO ALSO REACHES WARMER WATERS. THE
GFS MODEL SUGGESTS THIS REDUCTION IN SHEAR WILL OCCUR IN ABOUT
THREE DAYS...WHILE THE ECMWF MODEL WAITS UNTIL FOUR OR EVEN FIVE
DAYS FOR THIS TO OCCUR. THIS DIFFERENCE LEADS TO SUBSTANTIAL
UNCERTAINTY IN HOW MUCH OF A CYCLONE WILL REMAIN AND WHETHER IT
WILL SIGNIFICANTLY RE-INTENSIFY LATE IN THE PERIOD. THE INTENSITY
FORECAST IS VERY SIMILAR TO THE PREVIOUS ADVISORY AND IS CLOSE TO
THE CONSENSUS IN THE FIRST THREE DAYS AND BELOW IT THEREAFTER.
HUMBERTO HAS BEEN MOVING AT 10 KT TOWARD THE NORTH-NORTHWEST...AS IT
IS PROGRESSING THROUGH A BREAK IN THE MID-LEVEL RIDGE. IN ABOUT A
DAY...A STRONG DEEP-LAYER RIDGE REBUILDS NEAR THE AZORES AND
SHOULD ABRUPTLY TURN HUMBERTO TOWARD THE WEST-NORTHWEST. BY DAY
FIVE...HUMBERTO SHOULD BE ROUNDING THIS RIDGE AND BEGINNING
RECURVATURE. THE TRACK MODELS ARE TIGHTLY CLUSTERED...BUT ARE
SOMEWHAT FASTER AND FARTHER NORTH THAN THE PREVIOUS CYCLE. THE
TRACK FORECAST IS A BLEND OF THE LAST ADVISORY AND AN AVERAGE OF
THE GFS/ECMWF/FIM GLOBAL MODELS.
FORECAST POSITIONS AND MAX WINDS
INIT 13/0300Z 23.4N 29.7W 70 KT 80 MPH
12H 13/1200Z 24.4N 30.7W 65 KT 75 MPH
24H 14/0000Z 25.3N 32.8W 60 KT 70 MPH
36H 14/1200Z 26.2N 35.3W 50 KT 60 MPH
48H 15/0000Z 27.4N 37.6W 45 KT 50 MPH
72H 16/0000Z 29.5N 41.5W 45 KT 50 MPH
96H 17/0000Z 31.5N 44.0W 45 KT 50 MPH
120H 18/0000Z 34.5N 45.0W 50 KT 60 MPH
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FORECASTER LANDSEA
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